HOUSTON — Texas Republicans vote today to decide a contentious Senate primary, although late public polling suggests the contest could require a July 31 runoff to settle a battle that has pitted conservatives against each other.

Lt. Gov. David Dewhurst is the favorite in a crowded primary field and is expected to finish first when the votes are counted tonight. But former Texas Solicitor General Ted Cruz was in second and holding Dewhurst below 50 percent, according to a Public Policy Polling survey released Thursday that showed the lieutenant governor with a lead of 46 percent to 29 percent.

The battle between the two has been acrimonious and has left some voters here dissatisfied with their choices.

“You’re going to go into the poll to vote for Dewhurst or not to vote for Dewhurst,” said a Texas Republican insider unaffiliated with any of the candidates.

Texas’ unusual late spring primary has extended a campaign that is traditionally a quick affair held in early March. The television airwaves in recent weeks have become saturated with ads, often running back to back to back, while voters’ telephones have been ringing off the hook with robocalls. Sarah Palin, the 2008 GOP vice presidential nominee, recorded a call for Cruz; Fox News personality and former Arkansas Gov. Mike Huckabee did the same for Dewhurst.

The state’s primaries were delayed after the decennial redistricting process encountered legal challenges. Turnout during early voting has been low, adding to the uncertainty. With nearly 20 media markets, elections in Texas tend to be low on retail politicking and high on television and radio advertising, which usually decides a race.

Although Dewhurst and Cruz are expected to finish one-two, voters have been turned off by the constant sniping between them and the mostly negative attack ads that are running targeting each of the candidates. Some Texas Republicans say this unhappiness offers former Dallas Mayor Tom Leppert an outside shot at displacing Cruz and proceeding to a runoff. Leppert has generally been running third, but he was buoyed by the outcome of Nebraska’s GOP Senate primary.

In that contest, state Sen. Deb Fischer won after surging from third to first in the final weeks to upset frontrunner Jon Bruning and tea party favorite Don Stenberg. Nebraska Republicans turned to Fischer as an alternative to Bruning and Stenberg, who along with their supporters engaged in a bitter, negative campaign.

The Leppert campaign, well-funded and considered strong in his Dallas-Fort Worth home base, was “cautiously optimistic” heading into primary day.

“Leppert comes across as a grown-up, and he doesn’t seem angry,” the unaligned Texas GOP insider said, explaining the candidate’s appeal.

Also running in today’s primary is Craig James, a former ESPN analyst who played college football for Southern Methodist University while the school was still an NCAA football powerhouse. James also won a state championship playing high school football in suburban Houston. The first-time candidate’s existing notoriety does not appear to have translated into wide support. James’ role in the 2009 firing of Mike Leach as Texas Tech University football coach could have damaged his prospects.

The GOP nominee is considered a shoo-in to succeed Sen. Kay Bailey Hutchison, who decided to retire after losing the 2010 GOP gubernatorial primary to Gov. Rick Perry. In that contest, Perry assumed the role of tea party insurgent and was successful at painting Hutchison as an establishment Washington insider.

The conservative-activist establishment in Washington, D.C., eyeing an opportunity to bolster the ranks of tea-party-friendly Senators, has invested heavily in this primary in both cash and reputation and has much riding on the outcome. Republicans in Texas have long considered Dewhurst a stalwart conservative. He has the strong support of several Texas-based conservative groups, not to mention Perry.

But tea party activists who see Cruz as in the mold of Sen. Marco Rubio (Fla.) — both are ethnic Cubans — have targeted the lieutenant governor for being too cozy with the GOP establishment. The former solicitor general’s backers include the Club for Growth, FreedomWorks, Palin and Sens. Jim DeMint (S.C.) and Rand Paul (Ky.). Though Cruz has struggled at times, his supporters are optimistic about his chances in a runoff.

If Cruz faces Dewhurst in the runoff, his backers argue it would shape up as a repeat of the 2010 gubernatorial primary. It’s “Kay versus Rick all over again,” one source said.